This grant has the following objectives: (1) identify and characterize novel transcription factors in the human retina by molecular cloning and immunolocalization, and by biochemical studies of the recombinant proteins; (2) characterize regulatory DNA sequences that determine cone cell-specific expression of the human red-, green- and blue-sensitive visual pigment genes by determining the ability of these sequences to direct expression of linked reporter genes in transgenic mice; (3) construct transgenic mice in which defined retinal cell types have been ablated by selective expression of diphtheria toxin, both to study the physiological and developmental effects of this cell loss and as an aid to identifying cDNA clones specific for the target cells by differential screening. These three lines of research are expected to converge to elucidate the regulatory network of transcription factors and their targets. An additional result from this work will be a number of reagents--antibodies, cDNA and genomic clones, characterized regulatory sequences, and transgenic lines--that will be of general use to the retinal research community. While the proposed work is not targeted directly at human disease, past experience shows that elucidating normal mechanisms is a prerequisite for elucidating pathogenic mechanisms.